Boost sensor queries

[b33fy]

I've the Bosch boost sensor connected to a dash two, its on an impreza turbo engine albeit installed in a kitcar. the car seems faster than I anticipated and I'm concerned about it overboosting. the engine should boost at 0.9 bar maximum. The absolute presure side of things is confusing me a little, The dash shows .995 or so with just the ignition on and on tickover around .3, most of the time its below 1 bar unless I give it the hammer the maximum I've seen is about 1.7 / 1.8 bar I've had to replace the head gaskets in the last week or so and am not sure if this is due to overboost or just coincidence.

Sorry for going on a bit, just looking for a bit a reassurance and advice, does this sound about right to you guys?

[924RACR]

Suggestion - have you checked the cal on the sensor? You should be able to use a mighty-vac, with some creative matching of fittings etc, to apply at least that much pressure/vacuum... At least to get a sanity check, which seems to be what you're after.

Are you logging CAN signals from the ECU as well? You might have an ambient air pressure sensor as well, which might be useable as the reference signal to convert to relative pressure...

HTH...

[jeffw]

b33fy

As we already discussed your figures fit fine.

Ambient pressure with no engine on....0.995 Bar...spot on
Tickover.....under vacuum....0.3 Bar
going for it 1.7-1.9 Bar....again spot on if you take ambient away (1bar) you are making 0.7-0.8Bar boost.

Happy to talk this through with you again if you want.

[b33fy]

Suggestion - have you checked the cal on the sensor? You should be able to use a mighty-vac, with some creative matching of fittings etc, to apply at least that much pressure/vacuum... At least to get a sanity check, which seems to be what you're after.

Are you logging CAN signals from the ECU as well? You might have an ambient air pressure sensor as well, which might be useable as the reference signal to convert to relative pressure...

HTH...

Cheers 924, I do need a reference point so I've picked up a mechanical gauge for now to check it out as long as its in the same ballpark I'll be happy.

[b33fy]

lost a post somewhere.. oh well.

Thanks Jeff, I understand the principles behind absolute pressure though there is something niggling at me about this, the boost reading were al over the place today with the reading being 1.2 bar on tickover. it settled down though was showing positive pressure sooner than previously and boosting up to 2bar on the very odd occasion, wondering if the sensor is faulty as it always seemed slow to show positive boost (over 1bar) before. hope this makes sense, speak soon.

Mike